This invention relates to Schottky diodes and more specifically relates to a novel structure and process for manufacture of high temperature Schottkys which has a very high yield.
This invention is an improvement of the product and process described in U.S. Pat. No. 4,206,540 in the name of Herbert J. Gould, entitled "Schottky Diode and Method of Manufacture Using Palladium and Platinum Intermetallic Alloys and Titanium Barrier" and assigned to the assignee of the present application. The above patent describes a process for manufacturing a Schottky diode wherein either platinum or palladium is sintered into the surface of a silicon crystal to form a platinum or palladium silicide respectively. Thereafter the silicide is removed by etching with aqua regia. A single crystal layer is believed to remain on the silicon surface. The exact nature of the single crystal film which remains after the etching operation is not known.
It is believed however that the silicon surface is modified by the diffusion into it, to a depth of the order of tens of Angstrons, of palladium or platinum. For all practical purposes, the surface is a silicon surface in terms of its optical properties and in terms of its behavior with acids. However, the presence of the layer produces the extremely improved Schottky characteristics when contacted by a Schottky metal. Thus, the platinum or palladium silicide can be thought of as a doping source for the silicon substrate. After removal of the silicide, a conventional high work function material such as molybdenum, tungsten or chromium is applied over the single crystal film. The resulting Schottky barrier has excellent high temperature characteristics radically improved when compared to the same barrier metal, but on an untreated silicon surface.
When using platinum instead of palladium as the material for producing the silicide-treated surface, or single crystal film, the ultimately produced Schottky barrier has better high temperature characteristics. However, the yield during the manufacturing process is very low so that the process was not commercially feasible. In order to improve yield and as described in the patent, the platinum was encapsulated with a molybdenum layer over the top of the platinum. During the sintering operation the molybdenum acts as an oxygen barrier thus promoting the formation of silicide and yields using this process were improved, but are still low.